Means for maintaining liquid level in heat exchange apparatus



M. ASHLEY 2,678,547

C. MEANS FOR MAINTAINING LIQUID LEVEL IN HEAT EXCHANGE APPARATUSOriginal Filed Feb. 3, 1948 May 18, 1954 FIG.I

FIG. 5 g

Patented May 18, 1954 MEANS FOR MAINTAINING LIQUID LEVEL IN HEATEXCHANGE APPARATUS Carlyle M. Ashley, Fayetteville, N. Y., assignor toCarrier Corporation, Syracuse, N. Y., a corporation of Delaware Originalapplication February 3, 1948, Serial No. 6,083, new Patent No.2,581,466, dated January 8, 1952. Divided and this application November15, 1951, Serial No. 256,520

1 Claim.

This application is a division of my co-pending application Serial No.6,083, filed February 3, 1948, now Patent No. 2,581,466, entitled Meansfor Maintaining Liquid Level in Heat Exchange Apparatus, and relates toheat apparatus, more particularly, to automatic mean for preventing theliquid level in the evaporator or cooler of, for example, a centrifugalrefrigeration machine, from rising above a predetermined point underoverload conditions.

In centrifugal refrigeration systems, for example, a balanced charge ofrefrigerant is normally maintained in the evaporator. In use, however,as the load imposed upon the system increases, the amount of refrigerantgas trapped in the liquid in the evaporator increases. The increase inthe amount of gaseous refrigerant present in the evaporator decreasesthe density of the liquid refrigerant. The decrease in density of theliquid refrigerant results in a greater volume of refrigerant and anincrease in foam in the space above the tubes of the evaporator.Generally, eliminators are provided to break up the foam and to preventliquid carry-over to the compressor. The use of eliminators increasesthe cost of the system and in addition increases the amount of spacerequired. Without eliminators, however, the amount of space required toperform the same function is so great as to be impracticable undernormal conditions of use. The chief object of the present invention isto provide heat exchange apparatus in which carryover at high loads isprevented and increased capacity is obtained at low loads.

An object of the present invention is to provide a refrigeration systemincluding means for effectively preventing the liquid level in thecooler from rising above a predetermined point under overloadconditions.

A further object of the invention is to provide a refrigeration systemincluding means for automatically regulating the liquid level maintainedin the evaporator under all conditions of use.

A still further object i to provide a refrigeration system including acollecting chamber attached to the evaporator of the system, thecollecting chamber being effective for withdrawing a portion of theliquid refrigerant from the evaporator upon an increase in load toprevent a corresponding increase in the effective liquid levelmaintained inthe evaporator, and means for returning the withdrawnrefrigerant to the cooler when such conditions have ceased. Otherobjects of my invention Will be readily perceived from the followingdescription.

This invention relates to a refrigeration system including a compressor,a condenser, and an evaporator or cooler. As is well known, aneconomizer may be provided to reduce the cost of operation of system.Liquid refrigerant is collected in the evaporator and is placed in heatexchange relation with a medium to be cooled. Such medium passes througha coil disposed in the evaporator. The system is designed to opcrateupon a balanced refrigerant charge so that a predetermined quantity ofliquid refrigerant is present in the evaporator under normal loadconditions. As load imposed upon the system increases, the density ofthe liquid decreases due to trapping of gaseous refrigerant in the formof bubbles. Trapping of gaseous refrigerant within the pool of liquidrefrigerant maintained in the evaporator causes an increase in theeffective level of the liquid refrigerant; such increase or rise ineffective level of the liquid refrigerant results in a considerableincrease in the amount of foam present above the tubes of the evaporatorand permits carry-over to some extent of liquid refrigerant to thecompressor. In order to stabilize the level of refrigerant within theevaporator at a maximum point under overload conditions, a collectingchamber is provided disposed with its opening slightly above the toplevel of the coil and with its bottom at approximately the shutdownlevel of the liquid. Such chamber may be located within or without theevaporator. As the load imposed upon the system increases, the level offoam Within the evaporator increases until it is slightly above theopening leading to the collecting chamber. The foam then spills overinto the collecting chamber; the collectin cham,

ber eventually fills with liquid, thereby removing a portion of therefrigerant charge from active circulation in the system and stabilizingthe level of refrigerant in the evaporator at a predetermined point.Preferably, means are provided to return a portion or all of the liquidcollected in the collecting chamber to the evaporator when the loadimposed upon the system decreases.

The attached drawing illustrates a preferred embodiment of my invention,in which:

Figure 1 is a diagrammatic view of a centrifugal refrigeration systemembodying the present in vention;

Figure 2 is a sectional View through the evaporatorof the system shownin Figure 1 illustrating the collecting chamber;

Figure 3 is a view in elevation of the evaporator of the system shown inFigure 1;

Figure 4 is a sectional view of a modified form of evaporatorillustrating the collecting chamber disposed within the evaporator; and

Figure is a diagrammatic view illustrating the present inventionembodied in an absorption refrigeration system.

Referring to the drawing, the present invention is illustrated embodiedin a centrifugal refrigeration system of the type disclosed in JonesPatent No. 2,314,402, granted March 23, 1943. The system comprises anevaporator or cooler 2 connected to a centrifugal compressor 3 which inturn is connected to a condenser 4 by line 5. A plurality of tubes orcoils 6 are disposed in condenser 4. Cooling water is passed through thetubes 6 in heat exchange relation with compressed gaseous refrigerantforwarded to condenser 4 by compressor 3 to liquefy the same. Liquidrefrigerant from condenser 4 flows into an economizer l. Refrigerantfrom economizer '1 passes into cooler 2 and serves as make-uprefrigerant for the refrigerant being evaporated therein. Tubes or coils8 are disposed in cooler 2. A medium. to be cooled is passed through thetubes 3 in heat exchange relation with refrigerant in cooler 2; gaseousrefrigerant formed in cooler 2 passes to compressor 3, is compressed andagain forwarded to condenser 4.

To maintain a desired liquid level in cooler 2 even under conditions ofoverload of the system, a collecting chamber 9 is provided extending1ongitudinally of cooler 2. Preferably, chamber 9 is disposed Withoutthe shell of cooler 2. Suitable openings H! are formed above tubes 8 topermit foam within cooler 2 to flow into collecting chamher 3. Theopenings 10 to chamber 9 are disposed in such position within the cooler2 as to maintain a maximum liquid level within the cooler under overloadconditions. A line H connects chamber 9 with the bottom of cooler 2 topermit refrigerant condensed therein to be returned to the evaporator orcooler 2 as hereinafter described. A restriction |2 is disposed in lineH in order to regulate the quantity of refrigerant returning to thecooler. Preferably, restriction I2 is so designed as to limit returnedrefrigerant to such quantity as to balance the rate of collection, i.e., permitting an equivalent amount of liquid refrigerant to return tothe cooler to balance the amount of foam which spills over into thecollecting chamber.

In operation, conditioning medium flowing through the tubes 8 of cooler2 is warmer than the liquid refrigerant in the cooler. Consequently,heat is transferred from the conditioning medium to the liquidrefrigerant. This heat evaporates or boils off the refrigerant at atemperature corresponding to the pressure in the cooler. The refrigerantevaporated is drawn into the suction of compressor 3; the suction gas(gaseous refrigerant) is partially compressed by. the first stageimpeller of compressor 3 and then enters the second stage impeller ofthe compressor. Compression of the gaseous refrigerant is completed bythe following compressor stages and the compressed gas is dischargedinto condenser 4. Refrigerant discharged by compressor 3 into condenser4 condenses on the exterior of the condenser tubes 6 'at a temperaturecorresponding to condenser pressure. This temperature is higher thanthat of the water in tubes 6 so that the heat of condensation istransferred to the condenser water. Liquefied refrigerant drains fromcondenser 4 into economizer l and is supplied from economizer to cooler2 as previously described.

Assume an increase in load imposed upon the centrifugal system; suchincrease in load reduces the density of the liquid refrigerant withincooler 2 since gaseous refrigerant is trapped in the liquid in the formof bubbles. Trapping of gaseous refrigerant increases the volume ofrefrigerant within cooler 2 which results in a considerable increase inthe amount of foam present above tubes 3 of cooler 2. In order toprevent an increase in liquid refrigerant within cooler 2 beyond adesired point, collecting chamber is provided. Under overloadconditions, for example, the level of foam within cooler 2 increasesuntil it is slightly above the openings in leading to the collectingchamber 9. The foam then spills over into the collecting chamber 9through openings ill, thus maintaining a predetermined liquid levelwithin cooler 2. The collecting chamber 9 eventually fills with liquidrefrigerant thereby removing a portion of the refrigerant charge fromactive circulation in the system and stabilizing the level of therefrigerant in the evaporator at a predetermined point. As the loadimposed upon the system decreases, liquid refrigerant in chamher 9 isreturned to cooler 2 through line i l. Restriction i2 in line i l servesto regulate the quantity of refrigerant returned to cooler 2.

In the system described above, collecting chamher 9 is disposed withoutthe shell of cooler 2. in Figure 4, I have illustrated a modified formof my invention in which collecting chambers I3 are provided, suchchambers I3 being disposed within the shell of cooler 2 between the bankof coils 8 and the interior wall of the shell. Such chambers I; servethe same function as chamber 9 in that upon an increase in load imposedupon the system with a resulting decrease in density of refrigerantwithin cooler 2, excess foam spills over into chambers l 3 thusmaintaining the liquid level Within the cooler at a predetermined point.Such refrigerant may be returned to the cooler through restrictions 14therein as the load imposed upon the system decreases.

Figure 5 illustrates the present invention applied to an absorptionrefrigeration system. An absorption refrigeration system may include agenerator I5, condenser 15, absorber I1, and evaporator 18, connected bysuitable lines permitting flow of strong and weak solutions between suchelements of the system. A coil I9 is disposed in generator 15 and asuitable heating medium is passed therethrough in heat exchange relationwith solution in the generator. Such a system is shown diagrammaticallyin Figure 5. Condenser l6 and generator l5 are disposed in shell 2B. Acollecting chamber 2! is disposed adjacent generator [5 in shell [9;collecting chamber 2| is adapted to maintain the level of solution inthe generator at a predetermined point. When ebullition of solution inthe generator occurs, the density of the solution therein is decreasedand the level of solution in the gen erator rises, excess solutionspilling over into chamber 21. Solution from chamber 2! is not returneddirectly to the generator but is forwarded to the strong solution lineconnecting the generator and the absorber for supply to the absorber ofthe system.

The present invention provides a simple and effective means forregulating the liquid level within the cooler, generator or evaporatorof a refrigeration system under high and overload conditions. Theinvention may be applied to centrifugal, reciprocating and absorptionrefriger: ation systems. The invention permits complete submergence atlow load as well as preventing carry-over at high loads withoutsubstantial increase in the cost of the system. The means so providedpermits a reduction in the size of equipment required for a specificload and reduces the initial cost of the equipment by eliminating thevarious elements of the system heretofore required to prevent liquidcarry-over from the cooler to the compressor.

While I have described a preferred embodiment of the invention it willbe understood the invention is not limited thereto, since it may beotherwise embodied within the scope of the following claim.

I claim:

In an absorption refrigeration system the combination of an absorber, anevaporator, a, generator and a condenser disposed in a closed circuit, ashell containing the generator and condenser therein, with the condenserbeing placed above the generator, a coil in the generator through whicha heating medium is passed, a pool of solution in the generatorsurrounding at least a portion of the coil, ebullition of the :solutionoccurring during operation of the system thereby increasing the solutionlevel in the generator, a chamber in the shell to receive excesssolution when the solution level in the generator reaches a,predetermined maximum, and a line connecting the chamber to a strongsolution line of the system.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,352,814 Thomas July 4, 1944 2,461,513 Berestnefi Feb. 15,1949 2,552,071 Terrill May 8, 1951 2,581,466 Ashley Jan. 8, 1952

